1. Field of the Invention
The present invention relates to uretidione group-containing polyaddition products.
2. Description of the Prior Art
Polyaddition products containing uretidione groups are known and have been described, for example, in German OS No. 2,420,475. Such compounds are produced by reaction of the uretidione derived from toluene diisocyanate or hexamethylene diisocyanate with diols or diamines. The uretidione derived from isophorone diisocyanate also should be suitable for preparing the polyaddition compounds containing uretidione groups claimed in German OS No. 2,420,474; however, there are therein no examples or detailed disclosures.
The lack of examples and the like is not surprising, because the prerequisite for preparing a polyaddition compound containing uretidione groups is that the uretidione-containing diisocyanate, used for chain-extension with diols, have an NCO functionality of 2. When the NCO functionality of the uretidione-containing isocyanate is greater than 2, at least partial gelling has to be expected when it is reacted, for example, with diols.
With the dimerization catalysts of the prior art (tert. phosphines), it has not been possible until now to produce an isocyanurate-free uretidione dimer of isophorone diisocyanate (IPDI). A uretidione dimer of isophorone diisocyanate produced according to German OS No. 1,670,720 or OS No. 1,934,739 contains ca. 20-40% b.w. of the trimer of IPDI (isocyanurate of isophorone diisocyanate) in the mixture, depending on the reaction conditions. Such an uretidione dimer of isophorone diisocyanate containing isocyanurate cannot be considered for use in preparing valuable starting materials for polyurethane chemistry by further reaction, for example, with diols.
This further reaction could only be possible if pure, isocyanurate-free uretidione dimer of isophorone diisocyanate is used. The preparation of this material in pure form, free from admixed uretidione derivatives containing isocyanurate, and capable of being more than 98% decomposed back into isophorone diisocyanate by heating, is not the object of this patent application. The material is prepared by dimerizing isophorone diisocyanate, optionally in an inert organic solvent, with the help of a catalyst of the general formula: EQU X.sub.m P(NR.sub.2).sub.3-m
wherein
m=0, 1, 2 PA1 X: Cl, OR, R PA1 R: identical, different alkyl, aralkyl or (optionally substituted) cycloalkyl radicals, or 2R groups together form a ring with the N atom,
at temperatures of 0.degree.-80.degree. C., preferably 10.degree.-30.degree. C., and the resulting 1,3-diazacyclobutane-2,4-dione is isolated from the reaction mixture after 5-70% has reacted, preferably 20-50%, without previously deactivating the catalyst, as the residue of a thin film distillation and the catalyst and monomer are isolated as the distillate.
The uretidione dimer of IPDI produced in this manner is highly viscous at room temperature (&gt;10.sup.6 mPa.multidot.s; at 60.degree. C. 13.times.10.sup.3 mPa.multidot.s; at 80.degree. C. 1.4.times.10.sup.3 mPa.multidot.s). Its NCO content lies in the range of 16.8-18% NCO; i.e. greater or lesser proportions of polymeric uretidiones derived from IPDI must be present in the reaction product. The monomer content is &lt;1%. The NCO content of the reaction product after heating to 180.degree.-200.degree. C. is 37.1-37.7% NCO.
In the reaction of the uretidine dimers of IPDI with diols, the NCO/OH ratio should be 1:0.5-1:0.9 or 0.5:1-0.9:1. Depending on this ratio the uretidione-containing polyaddition products may contain free terminal NCO groups or, in special cases, terminal OH groups.
For certain applications it has proved convenient to react the free terminal NCO groups of the polyaddition product, the uretidione dimer of isophorone diisocyanate, with diols completely or at least partially with monoalcohols or primary or secondary monoamines.